This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Patent Application Serial No. 003916-4 filed in Sweden on Oct. 27, 2000, the entire content of which is hereby incorporated by reference.
The present invention relates to a drill string and a guide tube for mechanical handling in a rock drilling rig.
During drilling, especially in open-pit mining, the rock is frequently cracked due to previous explosions, such as is show in FIG. 1. Often the ground is made smooth by a thick layer of cracked rock 6, such that the drilling machine 1 shall be able to travel thereon at the drilling site. It is difficult to drill vertically straight in cracked rock, and therefore different solutions have been suggested to improve the straightness of the hole to be drilled. For instance, a guide tube 2 is provided in direct connection with the drill bit so as to guide the progress of the drill bit and increase the flushing speed outside and above the drill bit. The guide tube is about 4 to 6 meters long and comprises a male thread at its lower end (facing the drill bit) and a female thread 2a at its upper end (facing the machinexe2x80x94see FIG. 6). The tube has to be extended when drilling holes which are deeper than the length of the guide tube, preferably by means of rods that have smaller diameters than the tube with the intention to more simply allow passage of the drill dust.
A modern machine for drilling comprises a tong 3 (FIG. 2) for frictionally seizing a tube 2 close to the upper end of the tube 2 during extension and unscrewing. Frequently, the joint is strongly tightened during drilling and therefor the joint must be loosened by use of percussion in order to be unscrewed. During said loosening by use of percussion, which may continue for several minutes, the tube will slide relative to the shoes or clamping means 4 of the tong 3 which are clamping the tube as shown in FIG. 6 and furthermore, heat is developed in the joint. Consequently, the tube end is deformed and martensite is formed in the threads.
One object of the present invention is to provide a drill string and a guide tube for mechanical handling wherein the above-captioned drawbacks are counteracted.
Another object of the present invention is to provide a drill string and a guide tube for mechanical handling to simplify unscrewing of the thread joint in percussive rock tool equipment.
Still another object of the present invention is to provide a guide tube for mechanical handling which improves the life space of thread joints in percussive rock tool equipment.
The present invention relates to a guide tube adapted for use in a rock drill string. The guide tube comprises a main portion, a sleeve disposed at a first end of the main portion, and a male thread portion disposed at a second end of the main portion. The sleeve includes a recess having a female screw thread formed therein. A flush channel extends completely through the main portion of the male thread portion and communicates with the recess. The recess has a first length extending along a longitudinal axis of the guide tube. The main portion includes a section of reduced diameter disposed adjacent to first end of the main portion for defining a waist of narrower cross section than a maximum cross section of the sleeve. The waist has a length extending along the axis and is longer than the length of the recess.
The invention also pertains to a drill string for rock drilling, which includes the above-described guide tube.
Another aspect of the invention relates to a method of unscrewing a threaded joint between a member and a guide tube of a drill string. The guide tube comprises a main portion, a sleeve disposed at a first end of the main portion, and a male thread portion disposed at a second end of the main portion. The sleeve channel extends completely through the main portion and the male thread portion and communicates with the recess. The recess has a first length extending along a longitudinal axis of the guide tube. The main portion includes a section of reduced diameter disposed adjacent a first end of the main portion for defining a waist of narrower cross section than a maximum cross section of the sleeve. The waist has a length extending along the axis and is no longer than the length of the recess.
The method comprising the steps of:
A) positioning the sleeve above clamping shoes of a rig, wherein the clamping shoes engage the waist, and the sleeve rests upon the clamping shoes;
B) applying percussion to the threaded joint to loosen the thread connection; and
C) unscrewing the joint.